Pin constraints conflict with routing blockages or PG shapes. Who owns the fix?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Last updated:
Short Answer
The uncomfortable reality of this conflict is that both constraints can be individually valid and still be jointly impossible to satisfy at the same location — this isn't a case of one side simply being wrong. Ownership resolution starts by figuring out which constraint is actually authoritative here: package/interface intent, the block pin constraint itself, the routing blockage, or the PG reservation — and that's a negotiation between whoever owns each of those, not a unilateral PD call.
Technical Explanation
- Use the pin checks (exact reported layer/side/offset), the local blockage geometry, and the planned PG corridor layout together to see precisely where and how they collide.
- The resolution needs to preserve required function explicitly — if the pin carries a differential signal, a clock, or a supply connection, that functional requirement constrains what geometry changes are even acceptable, so keep those needs stated up front in the negotiation.
- This connects to the "return to owner" pattern elsewhere in this set — recognizing that a conflict needs cross-team negotiation rather than a silent local override is itself the correct PD judgment call.
Formula Or Decision Rule
Decision rule: the final pin has legal access and the blockage/PG purpose remains satisfied.
What To Check
- Warning sign: One team deletes the other team’s constraint locally.
- Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause.
- Correct: Return evidence to the interface, floorplan, or power owner, agree on the change, and rerun both checks.
Command Checks & Actions
- check_pin_placement -blocked_only true: checks pin-placement legality and access-related conditions
- report_pin_placement -pins <pins> -format {layer side offset}: reports pin layer, side, and offset
report_congestion-mode hot_spot: reports routing demand, capacity, overflow, or hot spots
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.
Healthy, Suspicious & Hard-stop Results
- Healthy: Identify whether package/interface intent, block pin constraints, routing blockage, or PG reservation is authoritative, then negotiate a geometry that preserves the required function.
- Hard stop: required legality or physical feasibility is missing or unexplained.
Common Mistake
The Trap: Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “Pin constraints conflict with routing blockages or PG shapes. ” to measurable physical evidence and an owned correction.
Follow-up Question & Model Response
"* Candidate Model Response: Model response: “I would change it if the same controlled rerun shows that one team deletes the other team’s constraint locally. ”
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